Custom Entry Points in WPF on .NET Core

To create a custom entry point for a WPF application that is created using the default template in Visual Studio and targets the .NET Framework, you can change the Build Action property of the App.xaml file from ApplicationDefinition to Page and create a class with a static Main method. That’s what I did in a previous post about handling protocol activation and redirection in packaged apps.

If you target .NET Core and try to do the same thing in Visual Studio 2019, you will get a dialog saying “Property is not valid” and some build errors that complains about duplicate ‘Compile’ and ‘Page’ items being included.

What you should do instead of changing the Build Action is to edit the .csproj project file (Project->Edit Project File in Visual Studio) and include a <StartupObject> element:

<PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <UseWPF>true</UseWPF>
    <StartupObject>WpfCoreApp1.Program</StartupObject>
</PropertyGroup> 

The value of the element refers to the fully qualified named of the class where the custom Main method is implemented:

namespace WpfCoreApp1
{
    class Program
    {
        [STAThread]
        static void Main()
        {
            App application = new App();
            application.InitializeComponent();
            application.Run();
        }
    }
}

The above implementation of the Main method is roughly the same as the one that is generated for you by the compiler if you don’t change anything after creating a new project in Visual Studio using the WPF App (.NET Core) template. If you put a breakpoint in it and start debugging, it should get hit when the application starts. You don’t need to do anything additional with the auto-generated App.xaml and App.xaml.cs files, i.e. you can add application-wide resources and implement custom startup logic in these files as usual.